They were, I used to use them all the time.
I think they must have been taken out though due to the increased damage/ vulnerability in this game. When someone used to bite on a TD feint in UFC 2 it would leave their head exposed allowing for a strike to be landed I believe.
If in UFC 3 biting on a TD feint meant leaving the head exposed for a free strike it'd be easy to win fights by feinting a TD into a head kick or flying knee where-as those strikes didn't do as much damage in UFC 2 so it wasn't as much of an issue.
I believe it'd be unbalanced if the same parameters were taken from UFC 2 and put into UFC 3 that's why it wasn't included initially. That's my thoughts on it anyway.
Though, if some time went into balancing for the new game it could definitely work I think and I'd love to see them return.